I did a search thru craigshelper this morning and while viewing the results, I got and HTTP 403 forbidden error. Then nothing would show up in the windows. I tried to access craigslist directly and I got the follow message: "This IP has been automatically blocked. Questions: email@example.com
Now I cannot access craigslist from any computer in my office. Anyone else having trouble.
Craigslist sometimes implements these automatic blocks when it gets a *lot* of requests from a single IP over a short period of time. (A lot generally means many hundreds of cities.) Most likely this happened to you because all of your office shares an IP address, and presumably several people there are searching craigslist. (Either that or you're doing several searches of the entire US a day, or you just got unlucky.)
Don't worry though - you have a couple of choices. First, the block should only last for a couple of days, so you could just wait it out. Second, you could send an email to that address they mention, and just say that you're getting this message. (Don't tell them that you were using CraigsHelper or searching a lot of cities.) They'll unblock you, but it may take a little while. Third, you can get a new IP address. Often you can do this by unplugging your cable/dsl modem, waiting 5 minutes, then plugging it back in. If not, you could google for how to reset your IP (but then it becomes a bit of an ordeal).
Hope that helps!